1. Technical Field
The present invention relates to a piezoelectric device, a liquid ejection head, and a liquid ejection apparatus and, in particular, to a piezoelectric device, a liquid ejection head, and a liquid ejection apparatus that include piezoelectric elements formed so that flexible surfaces are located between the piezoelectric elements and empty chambers.
2. Related Art
A piezoelectric device including piezoelectric elements is applied to various liquid ejection apparatuses, vibration sensors, or other equipment. For instance, a liquid ejection apparatus ejects (discharges) various liquids from a liquid ejection head by using the piezoelectric device. An example of the liquid ejection apparatus is an image recording apparatus such as an ink jet printer or an ink jet plotter. Since accurate placement of a small amount of liquid at a predetermined position has become possible, the liquid ejection apparatus is also applied to various manufacturing apparatuses. For instance, the liquid ejection apparatus is applied to a display manufacturing apparatus for manufacturing the color filters of liquid crystal displays or the like, an electrode forming apparatus for forming the electrodes of organic electroluminescence (EL) displays, field emission displays (FEDs), or the like, and a chip manufacturing apparatus for manufacturing biochips. A recording head for the image recording apparatus ejects liquid inks. A color material ejection head for the display manufacturing apparatus ejects the color material solutions of red (R), green (G), and blue (B). An electrode material ejection head for the electrode forming apparatus ejects liquid electrode materials. A bioorganic compound ejection head for the chip manufacturing apparatus ejects bioorganic compound solutions.
A liquid ejection head including the piezoelectric device causes pressure fluctuations in liquids in pressure chambers by driving the piezoelectric elements and ejects liquids through nozzles communicating with the pressure chambers. The pressure chambers are formed by performing anisotropic etching on a crystalline substrate such as a silicon substrate. The pressure chambers have portions formed of flexible components and serving as flexible surfaces. Lower electrodes, piezoelectric components formed of a piezoelectric material such as lead zirconate titanate (PZT), and an upper electrode are stacked above the flexible surfaces by a film formation technique. For instance, in the liquid ejection head disclosed in JP-A-2014-34114, the lower electrode of the upper and lower electrodes is patterned for each pressure chamber. Meanwhile, the upper electrode is a common electrode extending over more than one pressure chamber. By employing such a structure, piezoelectric components are mostly covered with the upper electrode. Thus, the upper electrode also functions as a protective film, thereby improving the moisture resistance of the piezoelectric components. In this structure, overlapping portions of the upper electrode, the piezoelectric components, and the lower electrodes in plan view (i.e., when viewed in the direction in which the layers are stacked) are active sections that deform when voltages are applied to the electrodes.
However, in the above structure, the active sections extend beyond the openings of the pressure chambers. Thus, application of a driving voltage to the upper and lower electrodes causes an electric field in end portions of the active sections outside the openings of the pressure chambers. This applies a force to move the end portions. However, a pressure chamber formation substrate has, under the end portions of the active sections, a structure or portions having no empty chamber such as a pressure chamber. Thus, the end portions of the active sections are virtually restrained from moving. This may cause cracking, flaking, or other damage in the end portions of the active sections due to stress concentration.